Zeolite Phi is defined and the method for its synthesis described in detail in U.S. Pat. No. 4,124,686, issued Nov. 7, 1978, to R. W. Grose et al. As disclosed therein, zeolite Phi is prepared hydrothermally from aqueous gels in the [N(CH.sub.3).sub.4 ].sub.2 O--Na.sub.2 O--Al.sub.2 O.sub.3 --SiO.sub.2 system. As synthesized, the zeolite exhibits large pore adsorption characteristics, has a composition expressed in terms of molar oxide ratios as EQU 1.0.+-.0.05 Na.sub.2 O:0.02-0.05 R.sub.2 O: Al.sub.2 O.sub.3 :4-7 SiO.sub.2 : 0-6 H.sub.2 O
wherein "R" represents the tetramethylammonium ion, and has a characteristic x-ray powder diffraction pattern containing at least the d-spacings shown in Table A below.
TABLE A ______________________________________ Interplanar Spacing d,A Relative Intensity ______________________________________ 11.6 .+-. 0.2 M 9.5 .+-. 0.2 S 7.00 .+-. 0.15 S 5.61 .+-. 0.10 S 5.04 .+-. 0.08 S 4.31 .+-. 0.08 S 3.43 .+-. 0.06 VS 2.92 .+-. 0.05 VS 2.61 .+-. 0.05 W 2.09 .+-. 0.05 W ______________________________________
In the expression of the relative intensity values, VS=very strong, S=strong, M=medium and W=weak. Evidence supporting the large-pore status of zeolite Phi includes adsorption data for (C.sub.4 F.sub.9).sub.3 N and neopentane, the latter being adsorbed on a calcined template-free form of zeolite Phi in an amount of 3.5 weight percent at a temperature of 25.degree. C. and a neopentane pressure of 750 torr. These data can be interpreted to mean that zeolite Phi contains 12-membered oxygen rings, a proposition further supported by data reported by Martens and Jacobs (ZEOLITES, 1986, vol. 6, September) derived from the bifunctional conversion of n-decane using Pt-loaded hydrogen forms of zeolite Phi. It is observed that in the x-ray diffraction pattern of the zeolite a number of the diffraction lines are broadened, suggesting a high degree of disorder in certain crystallographic directions and making a detailed elucidation of the crystal structure impossible.
In addition to the original synthesis of zeolite Phi using tetramethylammonium ions as the structure-directing agent, another synthesis using tetraethylammonium hydroxide (TEAOH) as the organic base and tetraethylorthosilicate as the silica source has been reported. In this regard see M. J. Franco et al, ZEOLITES, 1991, Vol. 11 April/May. In this synthesis the presence of potassium cations in the reaction mixture is said to be essential, but the K.sup.+ molar cation fraction must be below 0.1. In marked contrast with the Grose et al synthesis discussed above, the zeolite Phi composition of the synthesis using TEAOH is severely pore blocked due to stacking faults and consequently the void volume is not readily accessible to pyridine and m-xylene.